Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$127.67	13.183%	$144.5007	$144.50	$144.50	$144.50
Purchase #2	$239.69	12.456%	$269.5458	$269.55	$269.55	$269.50
Purchase #3	$138.39	12.536%	$155.7386	$155.74	$155.75	$155.70
Purchase #4	$210.51	7.111%	$225.4794	$225.48	$225.50	$225.50
Purchase #5	$142.34	5.460%	$150.1118	$150.11	$150.10	$150.10
Purchase #6	$170.70	6.566%	$181.9082	$181.91	$181.90	$181.90
Purchase #7	$187.56	3.839%	$194.7604	$194.76	$194.75	$194.80
7 purchase totals =	$1,216.86		$1,322.0449	$1,322.05	$1,322.05	$1,322.00